I just built a bridged LM3875 with Burrbrown's DRV134 chip. I heard strange "zzzzzzzzzzzzzzz" noise exactly like when we listen to an AM/FM tuner without station. The noise was not much loud and it remained on a particular level no matter how much I adjusted a volume knob.

- The output signal of DRV134 is feeded to each of LM3875 board.
- The schematic of LM3875 board is based on the picture below.
- Without bridge, the LM3875 board alone works perfectly.

I tried several things to get rid of the interference but I haven't found out the solution. (zobel network, inductor and ferrites in speaker cables, better power supply bypassing, caps in +/- pins in LM3875, different speakers, shielded and shorter speakercables etc. etc....). I hope to solve the problem by installing the amplifier pcb in the same enclosure with the power supply. Now the power supply is connected via braided cable which is about 0,5 metres long.

Funny thing is that the problem occurs only in one floor in my house. The interference is not coming from my house. I made sure of that by unplugging all other electricity from the house.

Do you have any potential interference sources like switched-mode power supply.